NEphron Sparing Treatment (NEST) for small renal masses: A feasibility cohort-embedded randomised controlled trial

Introduction & Objectives: A paucity of high level evidence on management of small renal tumours (cT1a, <4cm) is in part due to recruitment challenges of standard RCTs. Our objective was to assess if recruitment to a pragmatic, cohort‐embedded RCT comparing percutaneous cryoablation (CRA) and robot assisted partial nephrectomy (RPN) is feasible. Materials & Methods: Adults with T1a renal tumours were recruited to a longitudinal cohort study, consenting to long term follow up and patient reported outcome measures (ISRCTN18156881, funder NIHR RfPB PB‐PG‐0817‐20013). Additional eligibility criteria for an embedded, open‐label RCT were biopsy‐proven RCC considered suitable by the multidisciplinary team for both CRA and RPN. Eligible patients were randomised 1:1 to receive an invitation to consider CRA (intervention arm) or proceed with standard care, RPN (control arm). Patients were followed up to 6 months. The primary outcome was feasibility of recruitment to the RCT. 50 patients were needed to demonstrate consent rate of 30% (95%CI 11%). Secondary outcomes included participant retention, complications, length of hospital stay and change of renal function. Intention to treat analysis was performed. Results: From May 19‐July 21, 200 participants were recruited from a single specialist centre to the cohort. The primary endpoint of feasibility of recruitment into the embedded RCT was met with 50 patients (25% of the cohort (95%CI 19‐31%)). Of those invited to consider CRA 84% consented (CI 64‐95%) and 76% received CRA (CI 55‐91%). 100% of the control arm proceeded to RPN (CI 86‐100%). Figure 1 shows screened patients that were eligible, approached and consented. Patient demographics in the RCT were well balanced in terms of age, gender, tumour size, complexity and renal function. Retention was 90% (95% CI 79‐96%) at 6 months. Treatment complications at 30‐days were 3/25 (12%) for CRA v 7/25 (28%) for RPN, of which 0 v 2 were Clavien‐Dindo grade 3 or higher, respectively. Median length of hospital stay was shorter for cryoablation (1v2 days). Change in renal function at 6 months was ‐5.0 v ‐5.8 mls/min. [Figure presented] Conclusions: This single‐centre study demonstrates feasibility of recruitment to an open‐label cohort‐embedded RCT of CRA versus RPN for T1a renal tumours. Only 25% of the cohort were considered eligible for randomisation. These data inform future plans for a multi‐centre trial to provide level 1 evidence in this field.